Scott M. Grant
Centre for Sustainable Aquatic Resources, Marine Institute of Memorial University of Newfoundland
P. O. Box 4920, St. John's, Newfoundland, Canada A1C 5R3
Publication (Upload) date: 15 May 2006
GRANT, S. M. 2006. An exploratory fishing survey and biologial resource assessment of Atlantic hagfish (Myxine glutinosa) occurring on the Southwest slope of the Newfoundland Grand Bank. J. Northw. Atl. Fish. Sci., 36: 91–110. doi:10.2960/J.v36.m548
An exploratory Atlantic hagfish (Myxine glutinosa) survey was conducted on the southwest slope of the Newfoundland Grand Bank during autumn 2002 to collect samples for a biological resource assessment and investigate the selective properties of baited 227-litre traps with 12.7, 13.5, and 14.3 mm (1/2", 17/32", and 9/16") diameter escape holes. Atlantic hagfish were found to exhibit a juvenile hermaphroditic stage. Female Atlantic hagfish exhibited a total length (TL) at first, 50%, and 100% sexual maturity of 354, 378, and 440 mm, respectively. The testis was small and rudimentary showing no sign of maturation in the form of enlarged lobules in 350 hagfish examined within a size range of 195–638 mm TL. Each sexually mature female possessed a single clutch of developing ovoid eggs of similar size and 28% possessed both developing and degenerating eggs. Degenerating eggs were limited to the early stage of the reproductive cycle among females with developing eggs that were <12 mm in length. Examination of females with large (≥14 mm) eggs revealed a positive correlation (r2 = 0.61) between fecundity and total body length, however, the reproductive potential was low (11–38 eggs per female). Recent evidence of a seasonal reproductive cycle and current findings of a bimodal egg length-frequency distribution and the presence of several females with postovulatory follicles in a single point in time sample suggest there may be up to three synchronized spawning events per year on the Grand Bank. The intermediate status of the Grand Bank population with respect to maximum length, size at first attainment of sexual maturity, and body markings relative to populations in the eastern North Atlantic and continental shelf and slope waters of the eastern US corroborates the existence of clinal variants. Catches in control traps indicate a clear tendency for the average individual hagfish body size to increase with depth over a 146–664 m depth range. A length-weight relationship indicated the minimum marketable body weight coincides with a total length of 410 mm. The 14.3 mm trap consistently captured the lowest percentage of undersized (<410 mm TL) individuals. Studies suggest few hagfish will survive when released, therefore it is recommended Grand Bank fishermen be encouraged to use traps with 14.3 mm escape holes or larger.
Key words: escape holes, hagfish, maturity, reproduction, survey, traps